This invention relates to a gas and liquid contact body and to corrugated sheets of particular structure for forming a contact body. More especially, this invention relates to a contact body specifically adapted for use as heat transfer media in the form of wet deck fill in evaporative-type heat exchange apparatus, such as cooling towers, and particularly countercurrent evaporative heat exchangers, which are used for such applications as air conditioning and numerous other industrial processes. The contact bodies of the present invention are also useful as fill for gas scrubbers for reducing airborne pollution, media for trickling filters used in water and waste water treatment, and the like. This invention will be explained herein with reference to its primary intended use as wet deck fill in evaporative heat exchangers, such as cooling towers.
In usual cooling towers and other equipment comprising evaporative heat exchangers, water is distributed over the top of wet deck fill formed of contact bodies typically in the form of corrugated sheet material. As the water flows down the fill, a thin film of water is formed over the surface of the fill. A gas stream, usually air, passes over the water film on the fill to provide the evaporative cooling effect. Air flow is promoted with the use of a fan or centrifugal blower either from top to bottom (parallel flow), across the path of the water (crosscurrent) or in a direction opposite to the flow of the water, namely bottom to top (countercurrent).
The present invention may be used as fill in parallel flow, crosscurrent or countercurrent heat exchange apparatus, and is particularly effective when used in countercurrent applications.
The energy efficiency of an evaporative heat exchanger is determined in relation to its heat rejection capacity to its input energy, that is, the energy required to drive its blowers or fans for the air or other gas stream, as well as the pumps used to pump the water or other cooling liquid through the apparatus. Rising energy and building costs demand that heat exchange equipment manufacturers develop cooling towers and other equipment which is both more energy efficient and space efficient than prior art designs. In accordance with the present invention, efficiently and economically sized cooling towers or other evaporative heat exchangers are also more energy efficient. Thus, testing has shown that wet deck fill made of contact bodies using the corrugated contact sheets of the present invention has surprisingly lower pressure drop than fill using contact bodies made of corrugated contact sheets of the prior art. By lowering the pressure drop while maintaining excellent thermal performance, the same amount of air can be passed through the fill at lower fan or blower horsepower, allowing more economical thermal performance and energy efficiency for any fan system. Alternatively, if it is desired to use the same fan system as in prior art designs, wet deck fill made according to the present invention will perform at higher water loads and may be stacked higher within a heat exchanger to efficiently move air through the fill. This results in smaller towers of equal thermal capacity, providing the desired benefit of a cooling tower or other evaporative heat exchanger requiring less building space which can be manufactured more economically than prior art designs.
Contact bodies made from corrugated contact sheets of the present invention have excellent structural integrity and are easy to assemble from the contact sheets which can be made economically and efficiently. With the present invention, wet deck fill can be constructed to be placed in standard cooling towers on standard cooling tower fill supports. Contact bodies of the present invention can be stacked directly on each other to create layered wet deck fills without special intermediate supporting members which impede air flow and raise the pressure drop of the wet deck fill. Other advantages and benefits of the present invention will be set forth hereinafter following the description of the preferred embodiments of the present invention.
The prior art is crowded with various types of contact bodies assembled from contact sheets having different types and shapes of corrugations and various configurations.
Representative of prior art contact bodies which may be deemed to be relevant to the present invention are the following U.S. patents.
U.S. Pat. No. 2,809,818 discloses in the paragraph bridging columns 4 and 5 that the contact body has lower edges forming a series of successive notches or serrations terminating in depending points 56, such that when viewed from the front (right side of the drawing), the lower edge looks like a series of "W"s extending over several vertical corrugations. The serrated lower edge is to prevent water dams from forming which would result in a high pressure drop. The contact body comprises alternating flat and corrugated sheets, where the corrugations are oriented vertically.
U.S. Pat. No. 2,986,379 discloses contact bodies used as a heat exchange core or wet deck fill made of sheets having vertical corrugations with serrated lower edges forming a series of "W"s as illustrated in FIGS. 4, 5 and 12 of the reference. The purpose of the serrated lower edges, as described in column 4, lines 30-34, is to increase the efficiency of the blower by facilitating discharge of water from the wet deck fill passageways. It appears that the corrugated sheets are sandwiched between intermediate planar sheets as generally illustrated in FIG. 2 of the reference. This reference also discloses that the sheets used to make the wet deck fill are of asbestos paper impregnated with a phenolic resin wherein the paper fibers preferably extend at right angles to the vertical passageways. The fibers are disclosed as functioning very effectively to diffuse water, to slightly impede its flow and to prevent the formation of any streams or rivulets (column 3, line 67 through column 4, line 11).
U.S. Pat. No. 3,084,918 discloses several embodiments of contact bodies characterized by alternating adjacent sheets forming the contact bodies having a bottom edge arranged in a staggered position with respect to the height of the adjacent sheet. The embodiments include either vertically corrugated sheets in contact with like vertically corrugated sheets or vertically corrugated sheets in contact with alternating flat sheets. The face-to-face adjacent corrugated sheets have their bottom edges at different elevations to prevent water collection at the bottom edges. The bottom edges of the flat and/or corrugated sheets may also be notched for the purpose of minimizing water collection at the bottom terminal edges. When viewed from the top or bottom, the sheets forming the contact body appear to form a regular geometric shape which extends straight through the contact body from the top to the bottom.
U.S. Pat. No. 3,099,696 discloses a gas and liquid contact body for use in a cooling tower made of a plurality of alternating sheets. One of the series of alternating sheets is a vertically corrugated sheet, and the other sheet of the series is planar. At column 2, lines 36-41, it is disclosed that the lower edges of the layers are cut off in an inclined manner along cutting surfaces 18 (FIG. 1 of the reference) to facilitate flowing off of the water and, thus, prevent the cross sectional area of the channels to be bridged over and clogged at the lower end by drops of water.
U.S. Pat. No. 3,265,550 discloses a contact body or packing element for use in a cooling tower or the like. Although the drawings and most of the description relate to a contact body having alternating planar and vertically corrugated sheets, the last paragraph of column 4 states that all of the sheets may be corrugated. The bottom edges of all sheets are cut to form serrations extending over several vertical corrugations, resulting in a series of drainage tips 16 (FIG. 1 of the reference) to assure continuous drainage.
U.S. Pat. No. 3,526,393 discloses a contact body for use in a cooling tower wherein the contact body has vertically oriented sheets having angled corrugations where the angle of corrugation is maintained throughout the height of the sheets. Adjacent sheets are aligned such that the corrugations criss-cross. The lower edges of the sheets are formed with projections or serrations 36 (FIGS. 2 and 3 of the reference) which are formed by cutting the bottom edges with a saw blade inclined relative to the edges at an acute angle and the sheets are formed as indicated in the last paragraph of column 2 with further reference to the manufacturing technique of U.S. Pat. No. 3,470,280. The resulting inclined surfaces 38 of the serrations at the bottom edges have an angle substantially less than 45.degree., such as from 15 to 30.degree. coinciding with the ridges of the corrugations or folds so that the length of the points or projections can be substantially greater than the height of the corrugations. These relationships result in the prevention of a damming or bridge effect by the water over the space between the sheets which would create an increase of pressure counteracting the passage of air as explained at column 3, lines 8-30.
A contact body which has been available commercially from AB Carl Munters under the trademark "ASBESdek.RTM." comprises a plurality of sheets having angled corrugations and bottom edges which are cut obliquely as generally indicated in U.S. Pat. No. 3,526,393. The bottom edges of the contact sheets in the commercial embodiment are not aligned in a regular honeycomb-like pattern or any other regular geometric pattern. Rather, the bottom angled and pointed edges are randomly aligned, although some of the peaks and troughs of the bottom edges portions randomly contact each other. Neither the top edge nor the bottom edge of the "ASBESdek.RTM." contact body is oriented generally vertically such that the axis of the portions of the corrugations are perpendicular to a horizontal plane.
U.S. Pat. No. 3,540,702 discloses a contact body for cooling towers or the like made of adjacent sheets having horizontally oriented major corrugations. Minor corrugations are formed at oblique and opposite angles within each of the walls forming the major corrugations.
U.S. Pat. No. 3,599,943 discloses a contact body for use in a crosscurrent cooling tower in which air or other gas flows in a substantial horizontal direction across the path of the flow of water of other liquid in a substantially vertical direction. The contact body comprises a plurality of corrugated sheets wherein the corrugations of adjacent sheets extend diagonally criss-cross with respect to each other. The apices of the corrugations appear to be aligned at the left-hand side of the contact body as seen in FIGS. 1 and 3 of the reference.
U.S. Pat. No. 3,738,626 discloses a contact body for use in cooling towers or the like composed of corrugated layers in which the corrugations in adjacent layers form an angle relative to each other and extend at an inclined angle toward a lower liquid discharge edge. The bottom edges of the corrugated sheets forming the contact body are cut and arranged as illustrated in FIGS. 2 and 3 of the reference and as described in the Summary of the Invention and in the paragraph bridging columns 2 and 3 of the reference, to counteract collection of liquid due to the combined effect of surface tension and the upwardly streaming gas in a countercurrent-type heat exchanger.
U.S. Pat. No. 3,862,280 discloses a contact body for use in a crosscurrent or countercurrent cooling tower. The contact body comprises a plurality of corrugated sheets where the corrugations in adjacent sheets are disposed at an angle to each other. As illustrated in FIG. 1 of the reference, the bottom edges of the contact body used in a countercurrent cooling tower are serrated.
U.S. Pat. No. 4,296,050 discloses a contact body made of a plurality of corrugated plates or sheets which are provided with a plurality of apertures, as well as with a fine fluting on the walls of the corrugations. The flutings are disposed on both sides of the plates and are in the form of grooves which extend at an angle to the axis of the column which is of opposite sign to the angle of the corrugations relative to the axis of the column. The fine fluting on the plates improve liquid distribution over the plate surfaces by capillary action and channeling. The apertures interrupt or impede the channeling of water, thereby providing for a better water distribution over the sheets or plates forming the contact body. The lowermost series of substantially similarly constructed contact bodies or packing elements has a bottom configuration including serrations as best illustrated in FIG. 4 and explained at column 3, lines 12-17 of the reference.
U.S. Pat. Nos. 4,405,533 and 4,427,607 disclose contact bodies having particularly shaped top surfaces formed in a generally honeycomb pattern to allow for effective water spray between the sheets forming the contact bodies.
U.S. Pat. No. 4,459,244 discloses a contact body for use in cooling towers in which the contact body is comprised of a plurality of corrugated sheets where the corrugations of adjacent sheets criss-cross at an angle with respect to each other. The entire bottom surface of each contact body is cut at an angle across all of the corrugations. The bottom surface of the packing element appears to have an irregular honeycomb-type of pattern as illustrated in FIG. 4 of the reference. Since the bottom of the contact body forms a V-shape by virtue of obliquely cut sheet members forming the contact body, the water will flow along the edges of the obliquely cut members down to the surface of a central reinforcing plate 14 and thereafter down into a trough 16, rather than blocking the air passageways between adjacent sheets.
U.S. Pat. No. 4,668,443 discloses a contact body comprising vertically oriented sheets having angled corrugations which criss-cross each other in adjacent sheets. As illustrated in FIGS. 1 and 2 of the reference, the angled walls forming the corrugations include a plurality of minor corrugations or other surface treatments, such as raised and/or lowered bars 16 oriented generally perpendicular to the direction of the major face corrugations, as explained at column 11, lines 6-21 of the reference. In a commercial embodiment of the contact bodies made according to this patent by Brentwood Industries, Inc., each sheet of the contact body comprises a top portion and a bottom portion of corrugations having axes that are perpendicular, rather than at an oblique angle to the horizontal. Moreover, when viewed from the top and bottom of the contact body, the corrugated sheets are arranged in a regular, honeycomb-like pattern. In some embodiments, the edges of alternating sheets are staggered in height with respect to each adjacent sheet in a manner as generally illustrated in FIG. 3 of U.S. Pat. No. 3,084,918, described above. The bottom edges of the sheets forming the contact body are not cut or beveled to have an inclined, serrated configuration.
Compared to the prior art, the present invention provides a contact body which has surprisingly enhanced thermal performance and operational characteristics, based on the structure and orientation of the sheets used to make the contact bodies.